Multi-starge compreessor including one or more reciprocatable pistons



Aug. 9, 1966 M. s. HUNT 3,265,294

MULTI-STAGE COMPRESSOR INCLUDING ONE OR MORE RECIPROCATABLE PISTONS Filed May 20, 1964 2 Sheets-Sheet 1 Aug; 9, 1966 M. s. HUNT 3,265,294

MULTI-STAGE COMPRESSOR INCLUDING ONE OR MORE RECIPROCATABLE PISTONS Filed May 20, 1964 2 Sheets-Sheet 2 United States Patent 3,265,294 MULTI-STAGE COMPRESSOR INCLUDING ONE OR MORE RECIPR-CECATABLE PETQNS Michael S. Hunt, Coventry, England, assignor to Bristol Siddeiey Engines Limited, Bristol, England Fiied May 20, 1964, Ser. No. 368,772 Claims priority, application Great Britain, May 24, 1963, 20,749/ 63 Claims. (Cl. 230-198) The invention relates to a multi-stage compressor including one or more reciprocatable pistons. An object of the invention is to provide a compact compressor and in particular to avoid the need for an interstage storage chamber outside the cylinder or cylinders in which the or each piston is positioned.

According to the invention, a multi-stage compressor including at least one compound piston, providing the stages of compression, is characterised in that the piston is provided with inlet and outlet valves communicating with an otherwise closed space or spaces within the piston, the valves being arranged to control the passage of working fluid from one stage of compression to the next and the or each space forming an interstage storage chamber.

The compressor may include a compound hollow piston, providing two stages of compression, the piston having a large diameter end portion and a co-axial smaller diameter end portion, each portion co-operating with corresponding end portions of a similarly shaped cylinder, the larger diameter end portion of the cylinder constituting the low pressure stage of compression and the smaller diameter end portion of the cylinder constituting the high pressure stage of compression, the annular shoulder between the two end portions of the cylinder having a valve therein operative to admit working fluid on induction strokes of the piston to the loW pressure stage of the cylinder, the annular shoulder between the two portions of the piston having a valve therein operative to discharge working fluid from the low pressure stage of the cylinder into the interstage storage chamber within the piston on compression strokes of the piston, the outer end wall of the smaller diameter end portion of the piston having a valve therein operative to discharge working fluid from the interstage storage chamber into the high pressure stage of the cylinder on induction strokes of the piston and the outer end wall of the smaller diameter end portion of the cylinder having a valve therein operative to permit discharge of working fluid from the high pressure stage of the cylinder on compression strokes of the piston.

Alternatively, the compressor may include a plurality of equi-angularly spaced cylinders extending radially from a common shaft and rotatable with the shaft, each cylinder containing a hollow compound piston, providing two stages of compression, the pistons and cylinders being in accordance with the immediately preceding paragraph also each piston being a free piston engaging at its radially-outer end against the inner periphery of a common annular casing around the cylinders, the casing being mounted, eccentrically of the shaft for rotation, when the shaft is rotated, by virtue of the engagement of outer ends of the pistons with the inner periphery of the casing, the pistons being reciprocatable in their respective cylinders as a result of the eccentric mounting of the casing.

The valves in the or each piston and its cylinder may conveniently be flap valves.

By way of example of the invention, a two-stage rotary compressor having six cylinders will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is an axial section through the compressor, and

FIGURE 2 is a section on the line II--II in FIG- URE 1.

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The compressor comprises six radially-extending and equi-angularly arranged cylinders integral with a hollow shaft 1, the interior of which communicates with the interiors of all the cylinders. Each cylinder has a radially-inner end portion 2, providing a high pressure stage of compression, and a radially-outer end portion 3 of larger diameter, providing a low pressure stage of compression and joined to the inner end portion byan annular shoulder 4. Each cylinder contains a similarly shaped hollow piston freely slidable within the compound cylinder. The radially-outer end 5 of each piston has a crown 6 which abuts the inner periphery of a common annular casing 7, mounted for rotation on bearings 8' carried by hub portions 9 of a stationary annular housing 11 enveloping the casing 7.. The hub portions 9 also carry bearings 10 in which the shaft 1 is mounted. The bearings 8 are eccentrically arranged with respect to the bearings 10, so that as the shaft 1 is rotated, the eccentricity of the casing 7 will cause the pistons to be reciprocated in their respective cylinders. The crowns 6 of the pistons will be held against the inner periphery of the casing 7 by the pressure of working fluid within the high pressure stage and by centrifugal force. The casing 7 has a ring of scoops 12, one being shown in FIGURE 1, on the outside of each of the end walls thereof. The scoops 12 communicate with ports 13 in the said end walls, whereby working fluid, e.g. carbon dioxide gas, will be admitted into the interior of the casing 7, as the latter rotates, from the interior of the housing 11. The working fluid is drawn in the direction of arrow X into the latter through an opening 14 in the peripheral wall of the housing 11.

A ring of ports 16 is provided in the annular shoulder 4 of each cylinder, these ports being covered by an annular flap valve 17 (see FIGURE 1) which closes on the radially inward (ie the compression) stroke of the piston and opens on the radially-outward (i.e. the induction) stroke, so that during the latter stroke, working fluid is drawn from the interior of the casing 7 into the low pressure stage of the cylinder. Each piston has an annular shoulder 18 between the larger diameter end portion 5 and the smaller diameter end portion 19 thereof, the annular shoulder 18 being provided with a ring of ports 20, which are covered by an annular flap valve 21. The latter opens during the radially-inward stroke of the piston and closes during the radially-outward stroke thereof, so that during the radially-inward stroke, the flap valve 21 will permit the transfer of working fluid from the low pressure stage into an interstage storage chamber 22, provided within the hollow piston. The radially-inner end face of each piston has a port 23 therein, which is covered by a flap valve 24, this closing during the radially-inward stroke of the piston and opening during the radially-outward stroke thereof,so that during the latter stroke, working fluid is admitted from the interstage storage chamber 22 into the high pressure stage of the cylinder. The radially-inner end wall of each cylinder has a port 25 therein, which is covered by a flap valve 26, this opening during the radially-inward stroke of the piston and closing during the radially-outward stroke thereof so that on the compressive radiallyinward stroke, working fluid from the high pressure stage of the cylinder is ejected therefrom into the hollow shaft 1 from which it is discharged in the direction of arrow Y.

The main advantage of this compressor is that by providing the interstage storage chamber 22 in the interio-r of each hollow piston, there is no need to provide a storage space externally of the cylinder, thus enabling the bulk of the compressor to be smaller than a known compressor of the same capacity. Also the rotary arrangement and shape of the cylinders enable the com- P-atented August 9, 1966- r 3 pressor to be accommodated in a small axial overall length.-

-Another advantage is that by using free pistons the construction of the compressor is simplified as it avoids any connecting rod or crank system. Also the valve arrangement is simple and provides a large valve area. Yet another advantage is that the compressor is in sub stantially complete rotary balance.

" Although the foregoing example shows six rotary cylinders, a compressor having any numbenof cylinders may be provided. For example a compressor may have a single stationary cylinder incorporating a compound two-stage piston, the cylinder and piston having Valves and an interstage storage chamber therewithin, similar to those illustrated.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A two-stage compressor including at least one compound piston providing said two stages of compression, the piston having a large diameter end portion and a co-axial smaller diameter end portion, a similarly shaped cylinder in which the piston is reciprocatable, the larger diameter end portion of the cylinder constituting the low pressure stage of compression and the smaller diameter end portion of the cylinder constituting the high pressure stage of compression, an annular shoulder between the two end portions of the cylinder, a first valve in said'annular shoulder of said cylinder operative to admit working fluid on induction strokes of the piston to the low pressure stage of the cylinder, an interstage storage chamber .within said piston, an annular shoulder between the two' portions of the piston, a second .valve in said annular shoulder of said piston operative to discharge working fluid from the low pressure stage of the cylinder 'into said interstage storage chamber on compression strokes of the piston, a third valve in the smaller diameter end portion of the piston operative to discharge working fluid from said interstage storage chamber into the high-pressure stage of the cylinder on induction strokes of the piston, and a fourth valve in the smaller diameter end portion of the cylinder operative to permit discharge of working fluid from the high pressure stage of the cylinder on compression strokes of the piston.

2. A two-stage, multi cylinder compressor comprising a rotatable shaft, a plurality of cylinders equi-angularly spaced and extending radially from said shaft and rotatable therewith, a free piston reciprocatable within each of said cylinders, each piston and each cylinder having a large diameter end portion and a co-axial smaller diameter end portion, the larger diameter end portion of the cylinder constituting a low pressure stage of compression and the smaller diameter end portion of the cylinder constituting a high pressure stage of compression, a common annular casing around said cylinders, the outer ends of all said pistons bearing against the inner periphery of said casing, a first bearing for said shaft, a second bearing for said casing, said second bearing providing an axis of rotation eccentric from the axis of rotation provided by said first bearing, an inlet for admitting working fluid into the interior of said casing, an annular shoulder between the two end portons of each said cylinder, a first valve in said annular shoulder of each said cylinder operative to admit working fluid from the interior of said casing on induction strokes of the pistons to the low pressure stage of said cylinder, an annular shoulder between the two end portions of an annular shoulder between the two portions of said piston, a second valve in said annular shoulder of each said piston operative to discharge working fluid from the low pressure stage of said cylinder into said interstage storage chamber on compression strokes of said piston, a third valve in the smaller diameter end portion of each said piston operative to discharge working fluid fromsaid interstage storage chamber into the high pres sure stage of said cylinder on induction strokes of said piston, and a fourth valve in the smaller diameter end portion of each said cylinder operative to permit discharge of working fluid from the high pressure stage of said cylinder on compression strokes of said piston.

3. A compressor as claimed in claim 2 in which each valve in each said piston and its cylinder is a flap valve...

the cylinder constituting a low pressure stage of compression andthe smaller diameter end portion of the cylinder constituting a high pressure stage of compression, at common annular casing around said cylinders, the outer ends'of' all said pistons bearing against the inner periphery of said casing, a first bearing for said shaft, a second bearing for said casing, said second bearing providing an axis of rotation eccentric from the axis of rotation provided by said first bearing, an inlet for admitting working fluid into the interior of said casing, a scoop mounted on the outside of said casing adjacent said inlet thereby to guide working fluid into said casing during the rotation of the latter, an annular shoulder between the two end portions of each said cylinder, a first valve in said annular shoulder of each said cylinder operative to admit working fluid from the interior of said casing on induction strokes of the pistons to the low pressure stage of said cylinder, an interstage storage cham ber within each said piston, an annular shoulder between the two portions of said piston, a second valve in said annular shoulder of each said piston operative to discharge working fluid from the low pressure stage of said cylinder into said interstage storage chamber on compression strokes of said piston, a third valve in the smaller diameter end portion of each said piston operative to discharge working fluid from said interstage storage chamber into the high pressure stage of said cylinder on induction strokes of said piston, and a fourth valve in the smaller diameter end portion of each said cylinder operative to permit discharge of working fluid from the high pressure stage of said cylinder on compression strokes of said piston.

5. A multi-stage compressor including at least one compound piston having at least two co-axial portions of different diameter and an annular shoulder interconnecting adjacent co-axial portions, a cylinder in which the piston is reciprocatable having portions of different diameter providing the stages of compression and an anular shoulder interconnecting adjacent portions of said cylinder, an interstage storage chamber within said piston, first inlet and outlet valves respectively controlling the flow of working fluid into a first cylinder portion, providing a first stage of compression, and the flow of Working fluid from said first cylinder portion into said interstage storage chamber and second inlet and outlet valves respectively controlling the flow of working fluid from said interstage storage chamber into a second cylinder portion, providing a second stage of compression, and the flow of working fluid from said second cylinder portion. a

References Cited by the Examiner UNITED STATES PATENTS 817,538 4/1906 Wixon 230-20l MARK M. NEWMAN, Primary Examiner. WARREN E. COLEMAN, Examiner. 

1. A TWO-STAGE COMPRESSOR INCLUDING AT LEAST ONE COMPOUND PISTON PROVIDING SAID TWO STAGES OF COMPRESSION, THE PISTON HAVING A LARGE DIAMETER END PORTION AND A CO-AXIAL SMALLER DIAMETER END PORTION, A SIMILARLY SHAPED CYLINDER IN WHICH THE PISTON IS RECIPROCATABLE, THE LARGER DIAMETER END PORTION OF THE CYLINDER CONSTITUTING THE LOW PRESSURE STAGE OF COMPRESSION AND THE SMALLER DIAMETER END PORTION OF THE CYLINDER CONSTITUTING THE HIGH PRESSURE STAGE OF COMPRESSION, AN ANNULAR SHOULDER BETWEEN THE TWO END PORTIONS OF THE CYLINDER, A FIRST VALVE IN SAID ANNULAR SHOULDER OF SAID CYLINDER OPERATIVE TO ADMIT WORKING FLUID ON INDUCTION STROKES OF THE PISTON TO THE LOW PRESSURE STAGE OF THE CYLINDER, AN INTERSTAGE STORAGE CHAMBER WITHIN SAID PISTON, AN ANNULAR SHOULDER BETWEEN THE TWO PORTIONS OF THE PISTON, A SECOND VALVE IN SAID ANNULAR SHOULDER OF SAID PISTON OPERATIVE TO DISCHARGE WORKING FLUID FROM THE LOW PRESSURE STAGE OF THE CYLINDER INTO SAID INTERSTAGE STORAGE CHAMBER ON COMPRESSION STROKES OF THE PISTON, A THIRD VALVE IN THE SMALLER DIAMETER END PORTION OF THE PISTON OPERATIVE TO DISCHARGE WORKING FLUID FROM SAID INTERSTAGE STORAGE CHAMBER INTO THE HIGH PRESSURE STAGE OF THE CYLINDER ON INDUCTION STROKES OF THE PISTON, AND A FOURTH VALVE IN THE SMALLER DIAMETER END PORTION OF THE CYLINDER OPERATIVE TO PERMIT DISCHARGE OF WORKING FLUID FROM THE HIGH PRESSURE STAGE OF THE CYLINDER ON COMPRESSION STROKES OF THE PISTON. 